2-methoxy-2-methylbutane

Endpoint summary

Additional information

Two closed bottle tests (OECD 301D) are available (Hazleton Europe, 1995; Slovnaft VÚRUP, a.s., 2005a). The percentage of biodegradation observed is ca. 5% after 7 days in both studies. There is good evidence for ready biodegradability when sewage sludge has become adapted to the substance. Such conditions will apply where there are continuous releases of TAME to a STP, such as for large production and processing sites. Thus, the substance can be assumed to be readily biodegradable in such cases. Therefore the characterisation of biodegradability in such STPs is set at “readily biodegradable” and the Monod kinetics are used for the degradation of TAME in the STP instead of the more simplified first-order kinetics as it can be assumed that the STPs at industrial site are carrying adapted sludge only. This also suggests that TAME is inherently biodegradable under certain conditions in the wider aquatic aerobic environment. However, the non-standard test data available indicate that TAME degradation might not fulfil the test criteria (OECD 302) to be classified “inherently biodegradable”. In contrast, adapted sewage sludge is able to rapidly degrade TAME.

Therefore, in the further assessment a distinction will be made between non-adapted municipal STPs which will be classified as “inherently biodegradable, not fulfilling criteria” and adapted industrial STPs where there are continuous releases of TAME which will be classified as “readily biodegradable”. For these adapted STPs the Monod kinetics are used for the degradation of TAME in the STP instead of the more simplified first-order kinetics.

 

In anaerobic, static sediment/water microcosms, TAME does not biodegrade (Suflita and Mormile, 1993; Mormile et al., 1994; Somsamak et al., 2001).

Based on the few studies available it should be concluded that rapid and reliable biodegradation of TAME in soil can not be assumed in any normal environmental conditions indicating very slow degradation in soil (Jensen and Arvin, 1990; Mormile et al., 1994; Zenker et al., 1999). The biodegradability of TAME in soil in aerobic and anaerobic conditions seems to be very slow and favourable conditions for degradation are difficult to attain.

 

The rate constant used in the assessment are:

Degradation in a non-adapted STP	0 d-1
Degradation in an adapted STP	Monod kinetics (default values)
Biodegradation in water	4.62E-03 d-1
Biodegradation in aerated sediment	2.31E-03 d-1
Biodegradation in soil	2.31E-03 d-1